Water-soluble complexes [(κ2-P,O-phosphinesulfonato)PdMe(L)] and their catalytic properties

Palladium(II) phosphinosulfonato methyl complexes [(PAO)PdMeL] (PΛO=κ²-P,O-2-(2-RC₆H₄) ₂PC₆H₄SO₃ with R = OMe (a), 2,6-(MeO)₂C₆H₃ (b)) rendered water-soluble by monodentate ligands L = tri(sodium phenylsulfonate)phosphine (TPPTS; 3a) and L = H₂N(CH₂CH₂O)_nMe (n= ca. 52, 4a, 4b) were prepared. While aqueous solutions of 3a are inactive toward ethylene, with 4a and, particularly, 4b very small particles of ca. 20 nm size of linear polyethylene are obtained, as anticipated. Catalyst activities and polymer molecular weights are low. This contrasts with the high polymerization activity of the amine complexes 4a, b and polymer molecular weights obtained in nonaqueous polymerizations in toluene. NMR spectroscopic studies reveal that the inactivity of 3a (also observed in nonaqueous polymerizations) is due to a lack of dissociation of the sulfonated phosphine from the Pd(II) center. The catalyst precursors 4a,b are stable in aqueous solutions, also at elevated temperature (70 °C). Decomposition occurs upon addition of ethylene monomer in the presence of water. These findings are supported by polymerization experiments with known lipophilic analogues of 3 and 4.